Quantitative Reconstruction of Late Miocene Monsoon‐Driven Climate and Hydrology in the Himalayan Foreland, Nepal

The Late Miocene was a critical interval in the evolution of the South Asian monsoon system and the Himalayan foreland. This study presents a quantitative paleoclimatic reconstruction based on fossil leaf assemblages from the Lower (10.5–9.2 Ma) and Middle (9.2–7.0 Ma) Siwalik sediments of the Daldale section, western Nepal, using the Climate Leaf Analysis Multivariate Program (CLAMP). The reconstructed mean annual temperatures are 22.2 ± 2.3°C for the Lower Siwalik and 21.5 ± 2.3°C for the Middle Siwalik, with corresponding cold month mean temperatures of 15.4 ± 3.3°C and 15.0 ± 3.3°C. Mean annual precipitation ranges from 228 ± 48 to 238 ± 48 cm, and the annual vapor pressure deficit remains close to 6 ± 2 hPa, indicating persistently warm and humid monsoon‐influenced conditions throughout the study interval. Although several climatic variables exhibit coherent directional trends, including slightly lower temperatures, reduced rainfall concentration during the wettest months, and subtle changes in seasonal moisture availability in the Middle Siwalik, these differences largely overlap within the uncertainties of the CLAMP reconstructions. Consequently, the Daldale record indicates broad climatic stability rather than a major climatic transition between the Lower and Middle Siwalik intervals within the studied section. The study provides the first quantitative paleoclimatic benchmark for the Daldale Siwalik succession and demonstrates that climatic responses within the Himalayan foreland were spatially heterogeneous, with western Nepal maintaining persistently humid conditions despite broader regional environmental changes.